Benzodiazepines (BZDS) which bind to the benzodiazepine site (BZD-S) of the GABAA receptor are extremely effective anxiolytics, and are among the most widely prescribed psychoactive drugs in current therapeutic use. BZDs, however, also exhibit undesirable side effects including sedative and myorelaxant activity. Treatment with BZDs can also become considerably less effective over time (Woods et al., 1992, Pharmacol. Rev., 44:151-347).
Certain flavonoid compounds, for example, 5,7-dihydroxyflavone (also known as chrysin) and some chrysin derivatives, also bind to the BZD-S and are known to exhibit central nervous system effects including anticonvulsant effects and anxiolytic effects without also inducing either sedative or myorelaxant effects (U.S. Pat. No. 5,756,538 to Cassels et al. (1998)). Moreover, Scutellaria baicalensis Georgi (commonly known as Huang Qin in Chinese and Ougon in Japanese), an important medicinal herb in traditional Chinese medicine used in the treatment of anxiety, is known to contain chrysin and other naturally-occurring flavonoid compounds.
However, most flavonoids do not bind to the BZD-S with an affinity comparable to that of the BZDs. For example, chrysin demonstrates much weaker binding to the BZD-S than does diazepam. In addition, the identification and testing of those flavonoids with optimal binding properties has been hampered by the difficulty of preparing some of them in sufficient quantity. Many naturally-occurring flavonoids are present in plant materials only in minimal amounts. Moreover, the synthesis of highly active flavonoid compounds, such as those with a plurality of hydroxyl groups, has been particularly difficult because such compounds tend to form as intermediates in the synthesis of less active compounds, rather than as an end product.
The present invention is based, at least in part, on the identification of a class of flavonoid compounds with a high affinity for the BZD-S receptor. 2xe2x80x2 Hydroxyflavone and those 2xe2x80x2 hydroxyflavone derivatives which also contain a hydroxyl group at the 2xe2x80x2 position of the flavone general structure as shown in FIG. 1A, have demonstrated binding affinities for the BZD-S receptor far superior to the binding affinity of most flavonoid compounds. Some members of the class exhibit binding affinities comparable to those of BZDs, as much as one-hundred (100) times greater than that of a number of other flavonoid compounds. The high affinity of these compounds for the BZD-S receptor makes them useful for preventing and treating various central nervous system syndromes associated with the benzodiazepine site (BZD-S) of the GABAA receptor, such as anxiety and convulsions.
In one aspect, the present invention is directed to the use of the compounds of Formula I for preventing or treating a BZD-S associated syndrome: 
or physiologically acceptable salts thereof, wherein R5, R6, R7, R8, R3xe2x80x2, R4xe2x80x2, R5xe2x80x2 and R6xe2x80x2 are each, independently, H, OH, a C1-C6 alkyl, a C1-C6 alkenyl or a C1-C6 alkoxy. Alternatively, R5 and R6 taken together with the carbon atoms to which they are attached form a phenyl ring, which may be substituted or unsubstituted.
In particular embodiments, R5 is OH, R6 is OH or R7 is OH. In particular embodiments R5 and R6 are both OH, R6 and R7 are both OH or R5 and R7 are both OH. In a particular embodiment, R5, R6 and R7 are all OH.
In a particular embodiment, R8 is a C1-C6 alkoxy. In a particular embodiment, R6 and R8 are both a C1-C6 alkoxy. In a particular embodiment, R6 and R8 are methoxy.
In one particular embodiment, the invention is directed to a method of preventing or treating a BZD-S associated syndrome in a patient in need thereof including administering to the patient an effective non-toxic dose of a compound comprising 5,7,2xe2x80x2-trihydroxy-6,8-dimethoxyflavone (K36) or a physiologically acceptable salt thereof.
In a particular embodiment, the BZD-S associated syndrome is anxiety. In another particular embodiment, the BZD-S associated syndrome is convulsions.
In embodiments, the compounds utilized in the methods of the invention can be administered in a dose of a single aliquot. In alternative embodiments, the compounds utilized in the methods of the invention can be administered in a dose of two or more aliquots.
In another aspect, the compounds utilized in the methods of the invention can be used in the manufacture of a medicament for preventing or treating anxiety. In particular embodiments, the compounds utilized in the methods of the invention can be used in the manufacture of a medicament for preventing or treating anxiety without producing sedative and/or myorelaxant effects. In another embodiment, the compounds utilized in the methods of the invention can be used in the manufacture of a medicament for preventing or treating convulsions. A pharmaceutical package comprising one or more containers can be filled with the compound utilized in the methods of the invention. The package can further include instructions for using the compound in the prevention or treatment of anxiety. The package can further include instructions for using the compound in the prevention or treatment of convulsions.
In another aspect, the invention is directed to a method of preparing a compound of Formula I including extracting the compound from plant material known to contain the compound using a solvent; filtering the extract, concentrating the extract, successively purifying the extract, identifying and collecting the fraction containing the compound, and forming crystals of the compound from the concentrated extract. The crystals formed from the concentrated extract can have a purity of from about 90-99%. The product yield can be from about 5 mg to 10 mg per kg of plant material.
In another aspect, the invention is directed to the product obtainable by the methods of the invention. The product can be contained in a pharmaceutically acceptable formulation. A pharmaceutical package comprising one or more containers can be filled with the product obtainable by the methods of the invention. The package can further include instructions for using the product in the prevention or treatment of anxiety. The package can further include instructions for using the product in the prevention or treatment of convulsions.
In yet another aspect, the invention is directed to a method of identifying one or more compounds useful for preventing or treating a BZD-S associated syndrome, comprising assaying a population of compounds of varied chemical structure to determine the binding affinity exhibited by each compound for BZD-S; comparing the binding affinity exhibited by each member of the population of compounds for BZD-S binding affinity; and selecting at least one compound which contains the chemical structure that provides the strongest BZD-S binding affinity, wherein a compound that exhibits strong BZD-S binding affinity is useful for preventing or treating a BZD-S associated syndrome. The method of assaying the population of compounds can comprise determining the IC50 and K1 values of the members of the population of compounds. The method of assaying the population of compounds can further comprise determining the GABA ratios of the members of the population of compounds.